(a) Field of the Invention
The present invention relates to an electrode for a fuel cell system, a fuel cell including the same, and a method for preparing the same, and more particularly to an electrode which has a large surface area and thus improves electrochemical reaction, a fuel cell system including the same, and a method for preparing the same.
(b) Description of the Related Art
A fuel cell is a power generation system that generates electrical energy through an electrochemical redox reaction of an oxidant and a fuel such as hydrogen or a hydrocarbon-based material such as methanol, ethanol, or natural gas.
Fuel cells can be classified as phosphoric acid type, molten carbonate type, solid oxide type, polymer electrolyte type, or alkaline type cell depending on the kind of electrolyte used. Although each fuel cell effectively operates in accordance with the same basic principles, they may differ from one another in the kind of fuel, operating temperature, catalyst, and electrolyte used depending on the type of fuel cell.
Recently, polymer electrolyte membrane fuel cells (PEMFC) have been developed with power characteristics superior to those of conventional fuel cells, lower operating temperatures and faster starting and response characteristics. PEMFCs have advantages in that they can have a wide range of applications such as for mobile power sources for automobiles, distributed power sources for houses and public buildings, and for small electric sources for electronic devices.
A polymer electrolyte membrane fuel cell is generally composed of a stack, a reformer, a fuel tank, and a fuel pump. The fuel pump provides fuel stored in the fuel tank to the reformer. The reformer reforms the fuel to generate hydrogen and supplies the hydrogen to the stack. The stack forms the body of the polymer electrolyte fuel cell and is where the hydrogen is electrochemically oxidized and the oxidant is reduced to generate electrical energy.
A fuel cell may be a direct methanol fuel cell (DMFC) in which liquid methanol fuel is directly introduced to the stack. Consequently, the direct methanol fuel cell can omit the reformer which is essential for the polymer electrolyte fuel cell.
According to the above-mentioned fuel cell system, the stack generally includes several or a several tens of unit cells, each consisting of a membrane electrode assembly (MEA) and a separator (also referred to as a “bipolar plate”) laminated together. The membrane electrode assembly is composed of an anode (referred to as a “fuel electrode” or “oxidation electrode”) and a cathode (referred to as an “air electrode” or “reduction electrode”), separated by the polymer electrolyte membrane.
The separators not only work as passageways for supplying the fuel to the anode and the oxidant to the cathode, but they also work as a conductor, serially connecting the anode and the cathode in the membrane-electrode assembly. While the electrochemical oxidation reaction of the fuel occurs on the anode, the electrochemical reduction reaction of the oxidant occurs on the cathode, thereby producing electricity, heat, and water due to the migration of the electrons generated during this process.
The anode or cathode generally includes a platinum (Pt) catalyst. However, platinum is a rare and expensive metal and thus is not typically used in large amounts. In this regard, in order to reduce the amount of platinum, platinum supported on carbon is usually used.
The platinum supported on the carbon causes an increased thickness of the catalyst layer, and there is a limitation with respect to the amount of platinum that can be stored on the carbon. Additionally, contact between the catalytic layer and the membrane is not optimum, which deteriorates performance of the fuel cell.
Therefore, it is desirable to develop an electrode for a fuel cell that has reduced catalyst quantity in the catalyst layer but still shows excellent cell performance.